Osprey

The Osprey bird (Pandion haliaetus) is a medium-large raptor which is a specialist fish-eater with a worldwide distribution. It occurs in all continents around the world except for Antarctica, but in South America only as a non-breeding migrant. The Osprey bird is often known by other colloquial names such as ‘fishhawk’, ‘seahawk’ or ‘Fish Eagle’.

Because the Osprey bird is a species with many unique characteristics it has therefore been given its own taxonomic genus, Pandion, and family, Pandionidae.

The Osprey weighs around 1400 – 2000 grams (3 – 4.4 pounds) and has a length of 52 – 60 centimetres (20.5 – 24 inches). It has a 150 – 180 centimetres (5 – 5.9 feet) wingspan. The Osprey has mainly white underparts and head, apart from a dark mask through the eye, and fairly uniformly brown upperparts. Its short tail and long, narrow wings with four long ‘finger’ feathers (and a shorter fifth) give it a very distinctive appearance.

In flight, Ospreys have arched wings and drooping ‘hands’, giving them a gull-like appearance. Their call is a series of sharp whistles, cheep cheep, or yewk yewk. When Ospreys are near their nests, they vocal a frenzied ‘cheereek’.

The Ospeys diet consists mainly of fish. Fish they capture are generally 150 – 300 grams (5.3 – 10 oz) and measure about 25 – 35 centimetres (10 – 12 inches) in length. The Osprey is particularly well adapted to this diet, with reversible outer toes, closable nostrils to keep out water during dives, and backwards facing scales on the talons which act as barbs to help hold its catch.

The Osprey locates its prey from the air, often hovering prior to plunging feet-first into the water to seize a fish. As it rises back into flight the fish is turned head forward to reduce drag. The ‘barbed’ talons are such effective tools for grasping fish that, on occasion, an Osprey may be unable to release a fish that is heavier than expected. This can cause the Osprey to be pulled into the water. Rarely, Ospreys may prey on other wetland animals, such as reptiles (up to the size of young alligators), aquatic rodents, salamanders and other birds.

The Osprey breeds by freshwater lakes and sometimes on coastal brackish waters. Most Ospreys do not start breeding until they are five to seven years old. If there are no nesting sites available, young Ospreys may be forced to delay breeding. To ease this problem, posts may be erected to provide more sites suitable for nest building.

Osprey usually mate for life. In spring they begin a five-month period of partnership to raise their young. Female Osprey lay 3 – 4 eggs within a month and rely on the size of the nest to help conserve heat. The cinnamon-coloured eggs weigh about 65 grams (2.4oz). The eggs are incubated for about 5 weeks before they hatch.

The newly-hatched Osprey chicks weigh only 50 – 60 grams (2oz), but fledge within eight weeks. When food is scarce, the first chicks to hatch are most likely to survive.

Juvenile Osprey are identified by the buff fringes to the upperpart plumage, buff tone to the underparts and streaked crown. By spring, wear on the upperparts makes barring on the underwings and flight feathers a better indicator of young birds. Adult male Ospreys can be distinguished from female Osprey from their slimmer bodies and narrower wings. They also have a weaker or non-existent breast band than the female and more uniformly pale underwing coverts. The typical life span of the Osprey is 20 – 25 years.

Bubo owls and Bald Eagles (and possibly other eagles of comparable size) are the only major predators of both nests and adults. Ospreys have rarely been known to be preyed on by crocodiles when they dive into the water.

Twenty to thirty years ago, Ospreys in some regions faced possible extinction, because the species could not produce enough young to maintain the population. Possibly because of the banning of DDT (Dichloro-Diphenyl-Trichloroethane) and other dangerous pesticides in many countries in the early 1970’s, together with reduced persecution, the Ospreys, as well as other affected bird of prey species have made significant recoveries. 2007 IUCN Red List Category: Least Concern.